摘要
青藏高原地区广泛出露地幔橄榄岩体,但对其显微构造特征和矿物结构水的研究仍很缺乏。本文以马攸木地区雅江南带方辉橄榄岩为研究对象,采用光学显微镜、电子背散射衍射(EBSD)及傅里叶变换红外光谱(FTIR)对其进行系统分析。研究结果表明:(1)马攸木地区雅江南带方辉橄榄岩中橄榄石发育扭折带和波状消光,并具有显著的结晶学优选方位(A型组构),指示其主导变形机制为位错蠕变;(2)红外光谱测试表明,马攸木方辉橄榄岩中橄榄石几乎没有明显的结构水吸收峰,推断其经历了明显的H丢失。斜方辉石含水量处于85wt ppm^209wt ppm之间,代表地幔源区含水量或其下限值;(3)该区橄榄岩中橄榄石含水量低于包体和造山带橄榄岩中橄榄石含水量,斜方辉石结构水含量则与包体和造山带橄榄岩中斜方辉石的可以比较。我们的研究结果为了解青藏高原地幔橄榄岩中橄榄石的结构水和变形机制提供了初步资料。
Mantle peridotites are widely exposed in Tibet. However,little attention has been paid to the microstructural features and water contents of these peridotites. Here we carried out preliminary study on harzburgite from Mayoumu in the southern Yarlung Zangbo Suture Zone by virtue of optical microscope,electron backscattered diffraction（ EBSD） and Fourier transform infrared spectroscopy（ FTIR）. Our results suggest： 1） olivine shows significant intracrystalliine plasticity,including kink bands and undulatory extinction.Combined with the strong crystallographic preferred orientations（ CPOs）（ A-type fabric） of olivine,it is suggested that dislocation creep dominated the deformation of olivine; 2） FTIR results show olivine from the Mayoumu preidotite has almost no structurally-bound water,while orthopyroxene has a water content of 85 wt ppm - 209 wt ppm. We infer that olivine has suffered diffusion loss of H during exhumation of the peridotite body,while the measured water content in orthopyroxene probably represents the in situ content at depth or an equilibrium value after some diffusion loss; 3） The measured olivine water content in the Mayoumu peridotite is lower compared with those in olivine from xenolithic and orogenic peridotites,but the water content in orthopyroxene is comparable to those of orthopyroxene from xenolithic and orogenic peridotites. Our results highlight that the water content of constituent minerals in peridotite varies much as a function of geological settings and much attention is needed to be focused on the ophiolitic peridotite in the future.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第6期1653-1662,共10页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41372224)
中国地质调查局项目(1212011221066
1212011121224)联合资助
关键词
方辉橄榄岩
橄榄石
结晶学优选方位
结构水
西藏马攸木
Harzburgite
Olivine
Crystallographic preferred orientation
Water content
Mayoumu
Tibet
